U.S. patent number 5,500,109 [Application Number 08/324,305] was granted by the patent office on 1996-03-19 for method for preparing catalysts comprising zeolites extruded with an alumina binder.
This patent grant is currently assigned to Mobil Oil Corp.. Invention is credited to Kathleen M. Keville, Hye K. C. Timken, Robert A. Ware.
United States Patent |
5,500,109 |
Keville , et al. |
March 19, 1996 |
Method for preparing catalysts comprising zeolites extruded with an
alumina binder
Abstract
There is provided a method for preparing an alumina bound,
zeolite catalyst, wherein a zeolite of low silanol content is used
as the source of zeolite used to prepare the catalyst. A particular
zeolite used in this catalyst is zeolite Y. This catalyst may be
combined with at least one hydrogenation component and used to
hydrocrack hydrocarbons, such as gas oils. In particular, an
NiW/USY/alumina catalyst may be used in a hydrocracking reaction to
produce distillate boiling range hydrocarbons from higher boiling
hydrocarbons.
Inventors: |
Keville; Kathleen M. (Beaumont,
TX), Timken; Hye K. C. (Woodbury, NJ), Ware; Robert
A. (Wyndmoor, PA) |
Assignee: |
Mobil Oil Corp. (Fairfax,
VA)
|
Family
ID: |
22097591 |
Appl.
No.: |
08/324,305 |
Filed: |
October 17, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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70822 |
Jun 3, 1993 |
5378671 |
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Current U.S.
Class: |
208/111.3;
208/109; 208/108; 208/111.35 |
Current CPC
Class: |
B01J
29/084 (20130101); C10G 47/16 (20130101); B01J
29/70 (20130101) |
Current International
Class: |
B01J
29/00 (20060101); B01J 29/08 (20060101); C10G
47/16 (20060101); C10G 47/00 (20060101); B01J
29/70 (20060101); C10G 047/16 (); C10G 047/18 ();
C10G 047/20 () |
Field of
Search: |
;208/108,109,111
;502/85 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0251564 |
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Jan 1988 |
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EP |
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1108113 |
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Apr 1989 |
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JP |
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Primary Examiner: Cross; E. Rollins
Assistant Examiner: Griffin; Walter D.
Attorney, Agent or Firm: McKillop; Alexander J. Santini;
Dennis P. Kenehan, Jr.; Edward F.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a division of U.S. Application Ser. No.
08/070,822, filed Jun. 3, 1993, now U.S. Pat. No. 5,378,671 the
entire disclosure of which is expressly incorporated herein by
reference.
Claims
What is claimed is:
1. A process for hydrocracking a hydrocarbon feedstock, said
process comprising contacting said feedstock and hydrogen with a
hydrocracking catalyst under sufficient hydrocracking conditions,
said hydrocracking catalyst comprising a hydrogenation component
and an extrudate prepared according to a method for preparing an
alumina bound zeolite catalyst, said method comprising the steps
of:
(a) determining the silanol content of a zeolite;
(b) mulling together alumina, said zeolite of step (a), and water
under conditions sufficient to form an extrudable mass comprising
an intimate mixture of alumina and said zeolite;
(c) extruding the extrudable mass of step (b) under conditions
sufficient to form a green strength extrudate; and
(d) calcining the green strength extrudate of step (c) under
conditions sufficient to increase the crush strength of the
extrudate,
wherein said zeolite, which is introduced into mulling step (b),
has a silanol content of less than 10%, expressed in terms of
silicons included in silanols vs. total silicons.
2. A process according to claim 1, wherein said green strength
extrudate is calcined at a temperature of at least 400.degree. C.
in calcination step (d).
3. A process according to claim 1, wherein said alumina, which is
introduced into mulling step (b), is in the form of
pseudoboehmite.
4. A process according to claim 3, wherein alumina undergoes phase
transformation to gamma-alumina during calcination step (d).
5. A process according to claim 1, wherein said green strength
extrudate of step (c) is dried under conditions sufficient to
remove physically included water therefrom prior to calcination
step (d).
6. A process according to claim 5, wherein the drying of the
extrudate prior to step (d) takes place at a temperature of from
about 100.degree. C. to about 150.degree. C.
7. A process according to claim 1, wherein said zeolite is selected
from the group consisting of zeolite X, zeolite Y, zeolite beta,
mordenite, ZSM-20, and ZSM-10.
8. A process according to claim 1, wherein said zeolite is steamed
under conditions sufficient to reduce the silanol content thereof
prior to mulling step (b).
9. A process according to claim 1, wherein the silanol content of
the zeolite is measured by .sup.29 Si MAS NMR.
10. A process according to claim 1, wherein said hydrogenation
component is impregnated onto said extrudate either before or after
the calcination step (d).
11. A process according to claim 10, wherein said hydrocarbon
feedstock is a gas oil.
12. A process according to claim 11, wherein said gas oil has an
initial boiling point of at least 500.degree. F. and at least 90
wt. % of the hydrocarbons in said gas oil have a boiling point
greater than 650.degree. F.
13. A process according to claim 12, wherein the product of the
hydrocracking comprises at least 25 weight percent of a distillate
fraction having a boiling range of from 330.degree. F. to
650.degree. F. and wherein said distillate fraction is
recovered.
14. A process according to claim 13, wherein the zeolite is a
USY.
15. A process according to claim 14, wherein said hydrogenation
component comprises nickel and tungsten.
16. A process for hydrocracking a hydrocarbon feedstock, said
process comprising contacting said feedstock and hydrogen with a
hydrocracking catalyst under sufficient hydrocracking conditions,
said hydrocracking catalyst comprising a hydrogenation component
and an extrudate prepared according to a method for preparing an
alumina bound zeolite Y catalyst, said method comprising the steps
of:
(a) mulling together alumina, zeolite Y, and water under conditions
sufficient to form an extrudable mass comprising an intimate
mixture of alumina and zeolite Y;
(b) extruding the extrudable mass of step (a) under conditions
sufficient to form a green strength extrudate; and
(c) calcining the green strength extrudate of step (b) under
conditions sufficient to increase the crush strength of the
extrudate,
wherein said zeolite Y, which is introduced into mulling step (a),
has a silanol content of less than 10%, expressed in terms of
silicons included in silanols vs. total silicons.
17. A process according to claim 16, wherein said hydrocarbon
feedstock is a gas oil, and wherein said gas oil has an initial
boiling point of at least 500.degree. F. and at least 90 wt. % of
the hydrocarbons in said gas oil have a boiling point greater than
650.degree. F.
18. A process according to claim 17, wherein the product of the
hydrocracking comprises at least 25 weight percent of a distillate
fraction having a boiling range of from 330.degree. F. to
650.degree. F. and wherein said distillate fraction is
recovered.
19. A process according to claim 18, wherein the zeolite Y is a
USY, and wherein said hydrogenation component comprises nickel and
tungsten.
20. A process according to claim 16, wherein said hydrogenation
component comprises nickel and molybdenum.
21. A process according to claim 16, wherein said hydrogenation
component comprises palladium.
Description
BACKGROUND
There is provided a method for preparing an alumina bound, zeolite
catalyst, wherein a zeolite of low silanol content is used as the
source of zeolite used to prepare the catalyst. This catalyst may
be combined with at least one hydrogenation component and used to
hydrocrack hydrocarbons, such as gas oils.
Hydrocracking is a versatile petroleum refining process which
enjoys widespread use in the refining industry. Hydrocracking has
the ability to process a wide range of difficult feedstocks into a
variety of desirable products. Feedstocks which may be treated by
this process include heavy naphthas, kerosenes, refractory
catalytically cracked cycle stocks and high boiling virgin and
coker gas oils. At high severities, hydrocracking can convert these
materials to gasoline and lower boiling paraffins; lesser
severities permit the higher boiling feedstocks to be converted
into lighter distillates such as diesel fuels and aviation
kerosenes.
Hydrocracking is conventionally carried out at moderate
temperatures of 350.degree. C. to 450.degree. C. (650.degree. F. to
850.degree. F.), because the thermodynamics of the hydrocracking
process become unfavorable at higher temperatures. In addition,
high hydrogen pressures, usually at least 5600 kPa (800 psig) are
required to prevent catalyst aging and so to maintain sufficient
activity to enable the process to be operated with a fixed bed of
catalyst for periods of one to two years without the need for
regeneration.
The catalysts used for hydrocracking usually comprise a transition
metal such as nickel, cobalt, tungsten or molybdenum on an acidic
support such as alumina or silica-alumina although noble metals
such as platinum may also be used. Combinations of metals such as
nickel with tungsten have been found to be extremely effective with
a wide variety of feedstocks as has the presulfiding technique
which is now widely employed.
Hydrocracking processes using the hydrogen form of zeolite Y as the
acidic component are described, for example, in U.S. Pat. Nos.
3,269,934 and 3,524,809, and in "Preparation of Catalysts III", ed.
by G. Poncelet, P. Grange, and P. A. Jacobs, Elsevier Science
Publishers, 587 (1983).
SUMMARY
There is provided a method for preparing an alumina bound zeolite
catalyst, said method comprising the steps of:
(a) determining the silanol content of a zeolite;
(b) mulling together alumina, said zeolite of step (a), and water
under conditions sufficient to form an extrudable mass comprising
an intimate mixture of alumina and said zeolite;
(c) extruding the extrudable mass of step (b) under conditions
sufficient to form a green strength extrudate; and
(d) calcining the green strength extrudate of step (c) under
conditions sufficient to increase the crush strength of the
extrudate,
wherein said zeolite, which is introduced into mulling step (b),
has a silanol content of less than 10%, expressed in terms of
silicons containing silanols vs. total silicons.
There is also provided a method for preparing an alumina bound
zeolite Y catalyst, said method comprising the steps of:
(a) mulling together alumina, zeolite Y and water under conditions
sufficient to form an extrudable mass comprising an intimate
mixture of alumina and zeolite Y;
(b) extruding the extrudable mass of step (a) under conditions
sufficient to form a green strength extrudate; and
(c) calcining the green strength extrudate of step (b) under
conditions sufficient to increase the crush strength of the
extrudate,
wherein said zeolite Y, which is introduced into mulling step (a),
has a silanol content of less than 10%, expressed in terms of
silicons containing silanols vs. total silicons.
There are also provided catalysts prepared by the above
methods.
There is further provided a process for hydrocracking a hydrocarbon
feedstock, said process comprising contacting said feedstock and
hydrogen with a hydrocracking catalyst under sufficient
hydrocracking conditions, said hydrocracking catalyst comprising a
hydrogenation component and an extrudate prepared according to one
of the above-mentioned methods.
EMBODIMENTS
Improved catalysts comprised of siliceous zeolites in an alumina
binder are disclosed. The catalysts are prepared in such a manner
than enables low acidity, high SiO.sub.2/ Al.sub.2 O.sub.3 ratio
zeolites to be stabilized toward increases in acid activity that
arise from aluminum incorporation into the framework during the
alumina binding procedure. The catalysts may be prepared from
zeolites subjected to a thermal and/or hydrothermal treatment to
reduce crystal defect sites, such as silanol groups, prior to
contact with the alumina binder.
High silica/alumina ratio zeolites have been shown to be the
preferred catalysts for many hydrocarbon upgrading processes under
development for petroleum refining and petrochemical applications.
These processes include hydrocracking (MPHC) for maximum distillate
production. It has been found that high silica zeolites typically
exhibit an increase in acid activity when bound in alumina.
Alternate binding technology, such as silica binding as disclosed
in U.S. Pat. No. 4,582,815, could be used to avoid activation of
the zeolite by the binder. Activation of the zeolite by the alumina
binder has been attributed to alumina incorporation into the
zeolite framework which decreases the silica/alumina ratio and
increases the zeolite acidity, as disclosed by C. D. Chang, S. D.
Hellring, J. N. Miale, K. D. Schmitt, P. W. Brigandi, and E. L. Wu
in J. Chem. Soc., Faraday Trans., I, 81, 2215 (1985).
In many cases this activation has a detrimental impact on catalyst
performance. For example, the performance of VGO hydrocracking
catalysts comprised of large-pore zeolites disclosed in U.S. Pat.
No. 4,820,402 demonstrates a unique relationship between
selectivity to high value middle distillate products and increasing
zeolite silica/alumina ratio. Furthermore, the occurrence of
alumina binder activation in zeolites and the extent to which it
occurs have been difficult to predict.
Binding the zeolites with silica is currently one of the preferred
methods of eliminating this binder activation. In some
applications, however, silica binding may not be applicable such as
with bi-functional hydrocracking catalysts where a metal component
must be dispersed on the binder. It would be desirable, therefore,
to develop a procedure for preparing stable, low acidity zeolites
in alumina binder.
This present invention relates to the preparation of high silica
zeolite catalysts with improved resistance to alumina binder
activation. The procedure may involve a zeolite treatment, such as
mild steaming, to effect a reduction in structural defect sites
within the zeolite, such as zeolite silanol groups, prior to
contact with the alumina binder.
Previous investigators have identified defect sites, such as
silanols, in high silica zeolites, such as ZSM-5, using FT-IR and
.sup.29 Si MAS NMR as described by R. M. Dessau, K. D. Schmitt, G.
T. Kerr, G. L. Woolery, and L. B. Alemany in J. Catal., 104, 484
(1987). Hydrothermal treatment reduces the silanol content in ZSM-5
and this has been interpreted to occur through a silanol annealing
mechanism. However, the relationship between zeolite silanol
content and binder activation, and the necessity to control zeolite
silanol content prior to contact with the alumina binder has
heretofore not been recognized. The present invention describes an
improved procedure for manufacture of low acidity, high silica
zeolite catalysts in aluminum binder which may utilize a zeolite
treatment prior to contact with alumina binder. The treatment
provides benefits in terms of improved resistance of the zeolite to
alumina binder activation.
The present method first involves combining alumina, zeolite and
water in a mulling procedure. The amount of alumina should be an
amount which is sufficient to provide a sufficient amount of crush
strength to the ultimately produced extrudate. For example, the
amount of alumina may be 20-80 wt. % on a 100% solids basis. The
amount of zeolite should be an amount which is sufficient to
provide a sufficient amount of catalytic activity to the ultimately
produced catalyst. For example, the amount of zeolite may be 20-80
wt. % on a 100% solids basis. A sufficient amount of water should
be added to provide a sufficient amount of extrudability to the
solids in the mixture. For example, the amount of water may be
40-50 wt. % of the solids. This extrudable mixture may be in the
form of a paste. The alumina which is used to form this extrudable
mixture may be in the form of a hydrated alumina, such as
pseudoboehmite.
The zeolite, which is used to form the extrudable mass with alumina
and water, has a low silanol content. This silanol content may be
less than 10%, e g , less than 5% expressed in terms of silicons
containing silanols vs. total silicons. These percentages of
silanol content may be determined by .sup.29 Si MAS NMR. Silicon-29
NMR is an effective tool to determine the silanol content. A
.sup.29 Si NMR spectrum of a high-silica zeolite typically exhibits
three Si species corresponding to framework Si, silanol (SiOH), and
diol (Si(OH).sub.2). By integrating the areas of these peaks, the
silanol content can be determined. The method is described by E.
Lippmaa, M. Maegi, A. Samoson, M. Tarmamak, and G. Engelhardt in
the Am. Chem. Soc. 103, 4992, (1981). Other techniques that can
measure silanol content semi-quantitatively, including FT-IR and
proton NMR, can also be used.
It will be understood that, whenever the silanol content of a
zeolite is referred to herein, this silanol content is attributed
exclusively to silanols which are part of the zeolite framework and
excludes non-framework silanols, such as those which may be present
from amorphous silica impurities and/or occlusions, e.g., carried
over from the reaction mixture used to prepare the zeolite.
Zeolites which may be used to form catalysts by methods disclosed
herein include medium-pore size and large-pore size zeolites.
A convenient measure of the extent to which a zeolite provides
control of access to molecules of varying sizes to its internal
structure is the Constraint Index of the zeolite. Zeolites which
provide a highly restricted access to an egress from its internal
structure have a high value for the Constraint Index, and zeolites
of this kind usually have pores of small size, e.g., less than 5
Angstroms. On the other hand, zeolites which provide relatively
free access to the internal zeolite structure have a low value for
the Constraint Index, and usually pores of large size, e.g.,
greater than 8 Angstroms. The method by which Constraint Index is
determined is described fully in U.S. Pat. No. 4,016,218,
incorporated herein by reference for details of the method.
A zeolite which may be used in catalyst preparation described
herein may be a medium- or large-pore size zeolite. This zeolite
may have a Constraint Index of 12 or less. Zeolites having a
Constraint Index of 2-12 are generally regarded to be medium-pore
size zeolites. Zeolites having a Constraint Index of less than 1
are generally regarded to be large-pore size zeolites. Zeolites
having a Constraint Index of 1-2 may be regarded as either medium-
or large-pore size zeolites.
The members of the class of medium-pore size zeolites may have an
effective pore size of generally from about 5 to about 8 Angstroms,
such as to freely sorb normal hexane. In addition, the structures
provide constrained access to larger molecules. It is sometimes
possible to judge from a known crystal structure whether such
constrained access exists. For example, if the only pore windows in
a crystal are formed by 8-membered rings of silicon and aluminum
atoms, then access by molecules of larger cross-section than normal
hexane is excluded and the zeolite is not of the medium-pore size
type. Windows of 10-membered rings are preferred, although, in some
instances, excessive puckering of the rings or pore blockage may
render these zeolites ineffective.
Although 12-membered rings in theory would not offer sufficient
constraint to constitute a medium-size pore, it is noted that the
puckered 12-ring structure of TMA offretite does show some
constrained access. Other 12-ring structures may exist which may be
regarded to be medium-pore sized, and therefore, it is not the
present intention to classify a particular zeolite solely from
theoretical structural considerations.
Constraint Index (CI) values for some typical materials are:
______________________________________ CI (at test temperature)
______________________________________ ZSM-4 0.5 (316.degree. C.)
ZSM-5 6-8.3 (371.degree. C.-316.degree. C.) ZSM-11 5-8.7
(371.degree. C.-316.degree. C.) ZSM-12 2.3 (316.degree. C.) ZSM-20
0.5 (371.degree. C.) ZSM-22 7.3 (427.degree. C.) ZSM-23 9.1
(427.degree. C.) ZSM-34 50 (371.degree. C.) ZSM-35 4.5 (454.degree.
C.) ZSM-38 2 (510.degree. C.) ZSM-48 3.5 (538.degree. C.) ZSM-50
2.1 (427.degree. C.) TMA Offretite 3.7 (316.degree. C.) TEA
Mordenite 0.4 (316.degree. C.) Mordenite 0.5 (316.degree. C.)
Clinoptilolite 3.4 (510.degree. C.) Mordenite 0.5 (316.degree. C.)
REY 0.4 (316.degree. C.) Amorphous Silica--alumina 0.6 (538.degree.
C.) Dealuminized Y (Deal Y) 0.5 (510.degree. C.) Erionite 38
(316.degree. C.) Zeolite Beta 0.6-2.0 (316.degree. C.-399.degree.
C.) ______________________________________
The above-described Constraint Index provides a definition of those
zeolites which are particularly useful in the present catalysts.
The very nature of this parameter and the recited technique by
which it is determined, however, admit of the possibility that a
given zeolite can be tested under somewhat different conditions and
thereby exhibit different Constraint Indices. Constraint Index
seems to vary somewhat with severity of operations (conversion) and
the presence or absence of binders. Likewise, other variables, such
as crystal size of the zeolite, the presence of occluded
contaminants, etc., may affect the Constraint Index. Therefore, it
will be appreciated that it may be possible to so select test
conditions, e.g., temperature, as to establish more than one value
for the Constraint Index of a particular zeolite. This explains the
range of Constraint Indices for some zeolites, such as ZSM-5,
ZSM-11 and Beta.
It is to be realized that the above CI values typically
characterize the specified zeolites, but that such are the
cumulative result of several variables useful in the determination
and calculation thereof. Thus, for a given zeolite exhibiting a CI
value within the range of 1 to 12, depending on the temperature
employed during the test method within the range of 290.degree. C.
to about 538.degree. C., with accompanying conversion between 10%
and 60%, the CI may vary within the indicated range of 1 to 12.
Likewise, other variables such as the crystal size of the zeolite,
the presence of possibly occluded contaminants and binders
intimately combined with the zeolite may affect the CI. It will
accordingly be understood to those skilled in the art that the CI,
as utilized herein, while affording a highly useful means for
characterizing the zeolites of interest is approximate, taking into
consideration the manner of its determination, with the
possibility, in some instances, of compounding variable extremes.
However, in all instances, at a temperature within the
above-specified range of 290.degree. C. to about 538.degree. C.,
the CI will have a value for any given medium- or large-pore size
zeolite of 12 or less.
Examples of zeolites having a Constraint Index of from 1 to 12
include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, and
ZSM-48.
ZSM-5 is described in greater detail in U.S. Pat. Nos. 3,702,886
and Re. 29,948. The entire descriptions contained within those
patents, particularly the X-ray diffraction pattern of therein
disclosed ZSM-5, are incorporated herein by reference.
ZSM-11 is described in greater detail in U.S. Pat. No. 3,709,979.
That description, and in particular the X-ray diffraction pattern
of said ZSM-11, is incorporated herein by reference.
ZSM-12 is described in U.S. Pat. No. 3,832,449. That description,
and in particular the X-ray diffraction pattern disclosed therein,
is incorporated herein by reference.
ZSM-22 is described in U.S. Pat. No. 4,556,477, the entire contents
of which is incorporated herein by reference.
ZSM-23 is described in U.S. Pat. No. 4,076,842. The entire content
thereof, particularly the specification of the X-ray diffraction
pattern of the disclosed zeolite, is incorporated herein by
reference.
ZSM-35 is described in U.S. Pat. No. 4,016,245. The description of
that zeolite, and particularly the X-ray diffraction pattern
thereof, is incorporated herein by reference.
ZSM-38 is more particularly described in U.S. Pat. No. 4,406,859.
The description of that zeolite, and particularly the specified
X-ray diffraction pattern thereof, is incorporated herein by
reference.
ZSM-48 is more particularly described in U.S. Pat. No. 4,234,231,
the entire contents of which is incorporated herein by
reference.
The large-pore zeolites, including those zeolites having a
Constraint Index less than 2, are well known to the art and have a
pore size sufficiently large to admit the vast majority of
components normally found in a feed chargestock. The zeolites are
generally stated to have a pore size in excess of 7 Angstroms and
are represented by zeolites having the structure of, e.g., Zeolite
Beta, Zeolite Y, Ultrastable Y (USY), Dealuminized Y (Deal Y),
Mordenite, ZSM-3, ZSM-4, ZSM-10, ZSM-18, and ZSM-20. A crystalline
silicate zeolite well known in the art and useful in the present
invention is faujasite. The ZSM-20 zeolite resembles faujasite in
certain aspects of structure, but has a notably higher
silica/alumina ratio than faujasite, as does Deal Y.
Although zeolite Beta has a Constraint Index less than 2, it is to
be noted that it does not have the same structure as the other
large-pore zeolites, nor does it behave exactly like a large-pore
zeolite. However, zeolite Beta is a particularly preferred zeolite
for use in the present reaction.
ZSM-4 is described in U.S. Pat. No. 3,923,639.
ZSM-10 is described in U.S. Pat. No. 3,692,470.
ZSM-20 is described in U.S. Pat. No. 3,972,983.
Zeolite Beta is described in U.S. Pat. No. 3,308,069 and Re. No.
28,341.
Low sodium Ultrastable Y molecular sieve (USY) is described in U.S.
Pat. Nos. 3,293,192 and 3,449,070.
Dealuminized Y zeolite (Deal Y) may be prepared by the method found
in U.S. Pat. No. 3,442,795.
Zeolite UHP-Y is described in U.S. Pat. No. 4,401,556.
Another zeolite which may be used in the present catalyst is
MCM-22. MCM-22 is described in U.S. Pat. No. 4,954,325, as well as
in U.S. Pat. No. 5,107,054, the entire disclosures of which are
expressly incorporated herein by reference.
A particular zeolite for use in the present catalyst is zeolite
Y.
Zeolite Y is normally synthesized in forms having silica:alumina
ratios up to about 5:1. These as-synthesized forms of zeolite Y may
be subjected to various treatments to remove structural aluminum
therefrom. Many of these techniques rely upon the removal of
aluminum from the structural framework of the zeolite by chemical
agents appropriate to this end. A considerable amount of work on
the preparation of aluminum deficient faujasites has been performed
and is reviewed in Advances in Chemistry Series No. 121, Molecular
Sieves, G. T. Kerr, American Chemical Society (1973). Specific
methods for preparing dealuminized zeolites are described in the
following, and reference is made to them for details of the method:
Catalysis by Zeolites, International Symposium on Zeolites, Lyon,
Elsevier Scientific Publishing Co., (1980) (dealuminization of
zeolite Y with silicon tetrachloride); U.S. Pat. No. 3,442,795 and
G.B. No. 1,058,188 (hydrolysis and removal of aluminum by
chelation); G.B. No. 1,061,847 (acid extraction of aluminum); U.S.
Pat. No. 3,493,519 (aluminum removal by steaming and chelation);
U.S. Pat. No. 3,591,488 (aluminum removal by steaming); U.S. Pat.
No. 4,273,753 (dealuminization by silicon halide and oxyhalides);
U.S. Pat. No. 3,691,099 (aluminum extraction with acid); U.S. Pat.
No. 4,093,560 (dealuminization by treatment with salts); U.S. Pat.
No. 3,937,791 (aluminum removal with Cr(III) solutions); U.S. Pat.
No. 3,506,400 (steaming followed by chelation); U.S. Pat. No.
3,640,681 (extraction of aluminum with acetylacetonate followed by
dehydroxylation); U.S. Pat. No. 3,836,561 (removal of aluminum with
acid); DE-OS No. 2,510,740 (treatment of zeolite with chlorine or
chlorine-containing gases at high temperatures);NL No. 7,604,264
(acid extraction); JA No. 53,101,003 (treatment with EDTA or other
materials to remove aluminum); and J. Catal. 54, 295 (1978)
(hydrothermal treatment followed by acid extraction).
Highly siliceous forms of zeolite Y may be prepared by steaming or
by acid extraction of structural aluminum (or both) but because
zeolite Y in its normal, as-synthesized condition, is unstable to
acid, it must first be converted to an acidstable form. Methods for
doing this are known and one of the most common forms of
acid-resistant zeolite Y is known as "Ultrastable Y" (USY); it is
described in U.S. Pat. Nos. 3,293,192 and 3,402,996 and the
publication, Society of Chemical Engineering (London) Monograph
Molecular Sieves, 186 (1968) by C. V. McDaniel and P. K. Maher, and
reference is made to these for details of the zeolite and its
preparation. In general, "ultrastable" refers to Y-type zeolite
which is highly resistant to degradation of crystallinity by high
temperature and steam treatment and is characterized by a R.sub.2 O
content (wherein R is Na, K or any other alkali metal ion) of less
than 4 weight percent, preferably less than 1 weight percent, and a
unit cell size less than 24.5 Angstroms and a silica to alumina
mole ratio in the range of 3.5 to 7 or higher. The ultrastable form
of Y-type zeolite is obtained primarily by a substantial reduction
of the alkali metal ions and the unit cell size. The ultrastable
zeolite is identified both by the smaller unit cell and the low
alkali metal content in the crystal structure.
The ultrastable form of the Y-type zeolite can be prepared by
successively base exchanging a Y-type zeolite with an aqueous
solution of an ammonium salt, such as ammonium nitrate, until the
alkali metal content of the Y-type zeolite is reduced to less than
4 weight percent. The base exchanged zeolite is then calcined at a
temperature of 540.degree. C. to 800.degree. C. for up to several
hours, cooled and successively base exchanged with an aqueous
solution of an ammonium salt until the alkali metal content is
reduced to less than 1 weight percent, followed by washing and
calcination again at a temperature of 540.degree. C. to 800.degree.
C. to produce an ultrastable zeolite Y. The sequence of ion
exchange and heat treatment results in the substantial reduction of
the alkali metal content of the original zeolite and results in a
unit cell shrinkage which is believed to lead to the ultra high
stability of the resulting Y-type zeolite.
The ultrastable zeolite Y may then be extracted with acid to
produce a highly siliceous form of the zeolite.
Other methods for increasing the silica:alumina ratio of zeolite Y
by acid extraction are described in U.S. Pat. Nos. 4,218,307;
3,591,488 and 3,691,099 to which reference is made for details of
these methods.
In addition to the above-mentioned USY form of zeolite Y, other
known forms of zeolite Y, including the rare earth exchanged Y form
(REY), may be used in the present catalyst.
The zeolite Y used in the present catalyst may have a unit cell
size (UCS) of, for example, 24.5 Angstroms or less, e.g.,
24.15-24.50 Angstroms, e.g., 24.20-24.40 Angstroms. Such zeolites
having a low UCS, e.g., of 24.15-24.30 Angstroms, may be
particularly advantageous.
Zeolite Y with a low silanol content may be manufactured or
obtained directly from commercial vendors. The silanol content of
zeolites can be adjusted by various treatments including synthesis,
thermal or hydrothermal treatments as described in the previously
cited literature.
The extrudable mass may be passed through an extrusion die under
conditions sufficient to form cylindrical extrudates, which may, in
turn, be broken into pellets.
The strength of the extrudate pellets may ultimately be increased
to optimum levels by a calcination procedure. However, the
uncalcined extrudate has sufficient green strength to withstand the
usual handling procedures, which involve drying and possibly ion
exchanging and/or impregnating with sources of hydrogenation
components. Drying of the extrudate pellets may take place at
temperatures of from 100.degree. C. to 150.degree. C. This drying
procedure removes water which is physically included or associated
with the extrudate. Further water, termed chemically bound water,
may be removed from the extrudate upon calcination at higher
temperatures.
The crush strength of the green strength extrudate material is
improved by a calcination step. This calcination may take place at
a sufficient temperature, e.g., greater than 400.degree. C., for a
sufficient time, e.g., at least 1 hour, in an appropriate
atmosphere, e.g., nitrogen or air. This calcination may cause phase
transformation of the alumina binder to occur. More particularly,
the alumina binder may be transformed into the form of
gamma-alumina during this calcination step.
The extrudate catalyst may be combined with a hydrogenation
component or a source of a hydrogenation component either before or
after the calcination step. The hydrogenation component may be a
hydrogenation metal which may be a noble metal or metals, or a
non-noble metal or metals. Suitable noble metals include platinum,
palladium, and other members of the platinum group such as iridium
and rhodium. Suitable non-noble metals include those of Groups VA,
VIA and VIIIA of the Periodic Table. The Periodic Table used in
this specification is the table approved by IUPAC and the U.S.
National Bureau of Standards, as shown for instance in the table of
the Fisher Scientific Company, Catalog No. 5-702-10. Preferred
non-noble metals are molybdenum, tungsten, cobalt and nickel and
combinations of these metals such as cobalt-molybdenum,
nickel-molybdenum, nickel-tungsten and cobalt-nickel-tungsten.
Metal components may be pre-sulfided prior to use by exposure to a
sulfur-containing gas such as hydrogen sulfide at an elevated
temperature to convert the oxide form to the corresponding sulfide
form of the metal.
The metal may be incorporated into the catalyst by any suitable
method such as impregnation or exchange onto the extrudate. The
metal may be incorporated in the form of a cationic, anionic or
neutral complex such as Pt(NH.sub.3).sub.4.sup.2+ and cationic
complexes of this type will be found convenient for exchanging
metals onto the zeolite. Anionic complexes such as the molybdate or
metatungstate ions are useful for impregnating metals into the
catalysts.
The amount of the hydrogenation metal is suitably from 0.01 to 30
percent by weight, normally 0.1 to 20 percent by weight based on
the weight of the zeolite and matrix plus the weight of the
hydrogenation metal, although this will, of course, vary with the
nature of the component, less of the highly active noble metals,
particularly platinum, being required than of the less active base
metals.
The relative proportions of zeolite component and alumina matrix
may vary widely with the zeolite content ranging from between 1 to
99, more usually 5 to 80, percent by weight of the composite.
The hydrocracking process can be carried out at temperatures
ranging from about 250.degree. C. (480.degree. F.) to about
500.degree. C. (930.degree. F.), e.g., from about 300.degree. C.
(570.degree. F.) to about 450.degree. C. (840.degree. F.); hydrogen
pressures ranging from about 2 to 21 MPa, e.g., from about 3 to 21
MPa; liquid hourly space velocities ranging from about 0.05 to
about 10, e.g., from about 0.2 to 3; H.sub.2 circulations ranging
from about 500 to about 10,000 scfb, e.g., from about 2000 to about
6000 scfb.
The conversion may be conducted by contacting the feedstock with a
fixed stationary bed of catalyst, a fixed fluidized bed or with a
transport bed. A simple configuration is a trickle-bed operation in
which the feed is allowed to trickle through a stationary fixed
bed. With such a configuration, it is desirable to initiate the
reaction with fresh catalyst at a moderate temperature which is of
course raised as the catalyst ages, in order to maintain catalytic
activity.
A preliminary hydrotreating step to remove nitrogen and sulfur and
to saturate aromatics to naphthenes without substantial boiling
range conversion will usually improve catalyst performance and
permit lower temperatures, higher space velocities, lower pressures
or combinations of these conditions to be employed.
The present hydrocracking process may be used for hydrocracking a
variety of feedstocks such as crude petroleum, reduced crudes,
vacuum tower residua, coker gas oils, cycle oils, FCC tower
bottoms, vacuum gas oils, deasphalted residua and other heavy oils.
These feedstocks may optionally be subjected to a hydrotreating
treatment prior to being subjected to the present hydrocracking
process. The feedstock, especially in the non-hydrotreated form,
will contain a substantial amount boiling above 260.degree. C.
(500.degree. F.) and will normally have an initial boiling point of
about 290.degree. C. (about 550.degree. F.) more usually about
340.degree. C. (650.degree. F.). Typical boiling ranges will be
about 340.degree. C. to 565.degree. C. (650.degree. F. to
1050.degree. F.) or about 340.degree. C. to 510.degree. C.
(650.degree. F. to 950.degree. F.) but oils with a narrower boiling
range may, of course, also be processed, for example, those with a
boiling range of about 340.degree. C. to 455.degree. C.
(650.degree. F. to 850.degree. F.). Heavy gas oils are often of
this kind as are cycle oils and other non-residual materials. Oils
derived from coal, shale or tar sands may also be treated in this
way. It is possible to co-process materials boiling below
260.degree. C. (500.degree. F.) but they will be substantially
unconverted. Feedstocks containing lighter ends of this kind will
normally have an initial boiling point above 150.degree. C. (about
300.degree. F.). Feedstock components boiling in the range of
290.degree. to 340.degree. C. (about 550.degree. to 650.degree. F.)
can be converted to products boiling from 230.degree. C. to
290.degree. C. (about 450.degree. to 550.degree. F.) but the
heavier ends of the feedstock are converted preferentially to the
more volatile components and therefore the lighter ends may remain
unconverted unless the process severity is increased sufficiently
to convert the entire range of components. A particular hydrocarbon
feedstock which may be used is an FCC recycle oil having an initial
boiling point of at least about 343.degree. C. (650.degree. F.).
Other examples of feedstocks include those with relatively large
contents of non-aromatic hydrocarbons, such as paraffinic
feedstocks, e.g., feedstocks having at least 20 percent by weight,
e.g., at least 50 percent by weight, e.g., at least 60 percent by
weight, of paraffins. Feedstocks, including those which have been
hydrotreated, which may be used in the present process, include
those having at least 70 wt. % of hydrocarbons having a boiling
point of at least 204.degree. C. (400.degree. F.).
The hydrocarbon feedstock for the hydrocracking process may be a
gas oil. This gas oil may have an initial boiling point of at least
500.degree. F., and at least 90 wt. % of the hydrocarbons therein
may have a boiling point greater than 650.degree. F. This
hydrocracking process involving a gas oil feed may involve a net
production of a distillate fraction. For example, the product of
the hydrocracking reaction may have at least 25 wt. % of
hydrocarbons having a distillate boiling range of from 330.degree.
F. to 650.degree. F. The distillate fraction may be recovered,
preferably by a fractional distillation process.
EXAMPLE 1
Preparation of High Silica, Low Silanol USY Catalyst
Catalyst A
A commercial high silica USY zeolite containing essentially no
silanol groups as determined by Si-NMR was mulled in a 50/50 wt/wt.
mixture with alumina and extruded to prepare a formed mass. The
extruded mass was dried at 250.degree. F. and calcined for 3 hours
in 5 v/v/min. flowing air at 1000.degree. F. The calcined product
was then steamed at 1025.degree. F. for 24 hours in 1 atm steam.
The steamed extrudates were impregnated to incipient wetness with a
solution of ammonium metatungstate then treated in the following
stepwise manner: 1) dried at 250.degree. F. overnight and 2)
calcined for 2 hours at 1000.degree. F. in flowing air. This
calcined product was then impregnated to incipient wetness with a
nickel nitrate solution and steps 1-2 were repeated. The properties
of the final catalyst, labeled Catalyst A, are listed in Table
1.
EXAMPLE 2
Preparation of High Silica, High Silanol USY Catalyst
Catalyst B
A commercial high silica USY zeolite containing a high level of
silanol groups as determined by Si-MNR was combined in a 40/60
wt/wt. mixture with alumina and extruded to prepare a formed mass.
The extruded mass was dried at 250.degree. F. and calcined for 3
hours in 5 v/v/min. flowing air at 1000.degree. F. The calcined
extrudates were impregnated to incipient wetness with a solution of
ammonium metatungstate then treated in the following stepwise
manner: 1) dried at 250.degree. F. overnight and 2) calcined for 3
hours at 1000.degree. F. in flowing air. This calcined product was
then impregnated to incipient wetness with a nickel nitrate
solution and steps 1-2 were repeated. The properties of the final
catalyst, labeled Catalyst B, are listed in Table 1.
The properties of a hydrotreating catalyst, referred to in Example
3, are also listed in Table 1.
TABLE 1 ______________________________________ Catalyst Properties
Catalyst Catalyst Hydrotreating A B
______________________________________ Zeolite Properties SiO.sub.2
/Al.sub.2 O.sub.3 by NMR -- 220 200 Si as Silanols, -- .about.0 31
% (by Si-NMR) Unit Cell Size, Angstroms -- 24.25 24.28 Catalyst
Properties Zeolite, wt. % -- 50.sup.(1) 40.sup.(1) Zeolite Alpha in
-- 10 45 Al.sub.2 O.sub.3 binder Surface Area, m.sup.2 /g 138 335
252 Pore Volume, cc/g 0.39 0.56 0.48 Nickel, wt. % 3.9 3.9 3.7
Molybdenum, wt. % 13.7 -- -- Tungsten, wt. % -- 12.6 16.6
______________________________________ .sup.(1) Zeolite content in
alumina mixture prior to metals addition
EXAMPLE 3
This Example illustrates the yield advantage when hydrocracking a
Persian Gulf VGO with a hydrocracking catalyst prepared from USY
with low silanol content prepared in Example compared to that with
a similar catalyst prepared from USY with high silanol content
described in Example 2.
The experiments were carried out in a fixed-bed pilot unit
employing a commercial NiMo/Al.sub.2 O.sub.3 hydrotreating (HDT)
catalyst and the USY hydrocracking (HDC) catalyst. The pilot unit
was operated by cascading effluent from the HDT stage to the HDC
stage directly without removal of ammonia, hydrogen sulfide, and
light hydrocarbon gases at the interstage. The conditions employed
for the experiments included temperatures from
715.degree.-765.degree. F. (about 380.degree.-410.degree. C.), 0.5
LHSV (based on fresh feed relative to total HDT and HDC catalyst),
4000 scf/bbl (712 n.1. 1.sup.-1) of once-through hydrogen
circulation, and hydrogen inlet pressure of 815 psia (5.61 MPa).
The ratio of HDT to HDC catalyst was typically 1/2, vol/vol.
The feedstock for this Example was a nominal
650.degree.-1050.degree. F. (about 345.degree.-565.degree. C.)
Persian Gulf VGO (vacuum gas oil) having the properties shown in
Table 2 below.
TABLE 2 ______________________________________ Persian Gulf VGO
Feedstock Properties ______________________________________ General
Properties API Gravity 22.0 Hydrogen, wt. % 12.53 Sulfur, wt. %
2.53 Nitrogen, ppm 780 Pour point, .degree.F. 100 KV @ 40.degree.
C., cSt. 74.34 KV @ 100.degree. C., cSt. 7.122 Composition, wt. %
Paraffins 24.1 Naphthenes 22.1 Aromatics 53.8 Distillation,
.degree.F. (D2887) IBP 546 5% 627 10% 664 30% 760 50% 831 70% 906
90% 1003 95% 1041 EP 1158
______________________________________
Table 3 shows the improved performance of Catalyst A prepared from
low silanol USY compared to Catalyst B. At equivalent 650.degree. F
boiling range conversion, Catalyst A provides higher yield of
valuable distillate product (330.degree.-650.degree. F.) with lower
yield of light gas (C.sub.1 -C.sub.4) and naphtha (C.sub.5
-330.degree. F.). Hydrogen consumption is lower due to reduced
light gas product. Distillate selectivity, defined as distillate
yield/650.degree. F.+conversion, is 4% higher for Catalyst A.
TABLE 3 ______________________________________ Hydrocracking
Performance with Persian Gulf VGO Catalyst A Catalyst B
______________________________________ Temperature, .degree.F. 755
765 650.degree. F.+ Conversion, wt. % 40.9 40.7 Yields, wt. %
H.sub.2 S 2.5 2.7 NH.sub.3 0.1 0.1 C.sub.1 -C.sub.4 2.0 2.5 C.sub.5
-330.degree. F. 8.7 9.9 330-650.degree. F. 32.7 31.0 650.degree.
F.+ 54.7 54.9 H.sub.2 Consumption, scf/bbl 430 570 Distillate
Selectivity 80% 76% ______________________________________
(Distillate yield/650.degree. F.+ conversion)
* * * * *